Sunday, June 6, 2021

[Ichthyology • 2011] Chaetostoma formosae • A New Species of Chaetostoma Tschudi (Siluriformes: Loricariidae) from Colombia with A Definition of the C. anale Species Group

Chaetostoma formosae 
Ballen. 2011

Chaetostoma formosae sp. nov. is described from piedmont tributaries of the upper río Meta on the Cordillera Oriental in Colombia. The new species is distinguished from its congeners by the presence of an elongate unbranched anal-fin ray with two posterior dermal ridges in mature males, the presence of strongly recurved cheek odontodes, the presence of a parieto-supraoccipital dermal keel, the posterior margin of the pelvic-fin strongly projected and angulate in shape in mature males, and by details of coloration. The new species belongs to an informal monophyletic group herein called the Chaetostoma anale species group, along with two additional species, C. anale and C. jegui, from Colombia and Brazil respectively, based on an apomorphic modification of the anal fin in mature males.

Key-words: Systematics; Ancistrini; Andes; Sexual dimorphism; Taxonomy.

 Chaetostoma formosae sp. nov., holotype, ICNMHN 17114, adult male, 97.4 mm SL.
A) Dorsal view; B) Lateral view; C) Ventral view.
Note the enlarged anal fin in B and C. 
Scale bar equals 10 mm.

Chaetostoma formosae sp. nov.

Diagnosis: Chaetostoma formosae sp. nov. differs from all the species currently in Chaetostoma with the exception of Chaetostoma anale and Chaetostoma jegui by the presence in mature males of an enlarged second unbranched anal-fin ray bearing two distinct posterior dermal folds, and reaching the base of the caudal fin when fully developed (Figs. 1B, 3). Chaetostoma formosae differs from C. anale in having an angular distal pelvic-fin margin in mature males (vs. W-shaped distal margin in mature C. anale males, Figs. 1C, 4B), and the leading pelvic-fin ray neither elongate nor filamentous, not reaching beyond the adjacent branched ray in mature males (vs. leading pelvic-fin ray both enlarged and filamentous, longer than the remaining rays in mature males of C. anale). Chaetostoma formosae differs from C. jegui in having dark spots restricted to the head and the dorsal region surrounding the dorsal-fin base, and with compound pterotic and lateral plates bordered by dark pigment (vs. dark background with light blotches in C. jegui); and by the shape of the distal margin of the pelvic fin strongly projected and angular in mature males, vs. distal margin straight and with leading-fin ray sometimes surpassing the distal margin of the fin as evident in photographs).

Chaetostoma formosae further differs from Chaetostoma anomalum, C. breve, C. carrioni, C. dorsale, C. loborhynchos, C. machiquense, C. microps, C. nudirostre, C. platyrhynchus, and C. sovichthys by having a parieto-supraoccipital dermal keel (vs. skin on the parieto-supraoccipital unmodified in the form of a dermal keel in the cited species) and by the presence of strongly recurved cheek odontodes (vs. cheek odontodes straight in the same species cited above, Figs. 5 and 6). In addition, C. formosae differs from C. platyrhynchus by having an unplated snout (vs. snout plated in C. platyrhynchus).

Etymology: This species is named formosae, an adjective in genitive case derived from the latin formosa. The name honours my sister, Laura María Ballen, in recognition of her unconditional love and support to me.

Gustavo A. Ballen. 2021. A New Species of Chaetostoma Tschudi (Siluriformes: Loricariidae) from Colombia with A Definition of the C. anale Species Group. Pap. Avulsos Zool. 51(26); DOI: 10.1590/S0031-10492011002600001   

RESUMEN: Se describe Chaetostoma formosae, sp. nov. de tributarios pedimontanos del alto río Meta sobre la Cordillera Oriental en Colombia. La nueva especie se distingue de sus congéneres por la presencia de un radio alargado no ramificado en la aleta anal con dos carnosidades longitudinales posteriores en machos maduros, presencia de odontoides cefálicos fuertemente recurvados, presencia de una quilla carnosa parieto-supraoccipital, margen posterior de las aletas pélvicas fuertemente proyectado y de forma angular en machos maduros, así como detalles de coloración. Se propone que la nueva especie pertenece a un grupo monofilético informal llamado en el presente trabajo el grupo de especies Chaetostoma anale, junto con dos especies adicionales, C. anale y C. jegui, de Colombia y Brasil respectivamente, con base en una apomorfia de la aleta anal en machos maduros.
Palabras-clave: Sistemática; Ancistrini; Andes; Dimorfismo sexual; Taxonomía.